The present invention relates generally to valves and, more particularly, to a valve for controlling the pressurized flow of particles for an abrasive blasting machine or an agricultural, medical, pharmaceutical or other device.
Blasting machines, such as a sandblasting machine, use abrasive particles, such as powdered glass, sand or metal, to clean or prepare surfaces or objects for further treatment or use. For example, blasting machines are used as wire strippers to remove ceramic insulation from industrial-grade electrical wires so that the wires may be soldered or otherwise connected to electrical equipment.
A blasting machine typically features a nozzle arrangement that is directed at the surface or object to be cleaned or prepared. Abrasive particles are delivered to the nozzle arrangement of the blasting machine from a pressurized source through plastic or rubber tubing or hoses. The flow of abrasive particles to the blasting machine is conventionally controlled by a xe2x80x9cpinchxe2x80x9d type valve. More specifically, the pinch valve is used to squeeze the hose so that the flow of abrasive particles is closed off. To restore the flow of abrasive particles to the blasting machine nozzle, the pinch valve is manipulated so that the hose is released. Alternative pinch valve arrangements perform the same function by squeezing a rubber sleeve which is fitted in series with the abrasive hose.
Pinch valves are also used in applications other than abrasive blasting (e.g. agricultural, medical, pharmaceutical, etc.), and the present invention relates to those areas also.
A disadvantage of pinch valve arrangements, however, is that frequent replacement of the sleeve or hose is required. Typically, such replacements need to be carried out after a few thousand operations. If the sleeves or hoses are not replaced, they will fracture and allow pressurized particles to escape into the workplace. This can be a safety hazard.
As an alternative to pinch valves, xe2x80x9cneedlexe2x80x9d abrasive control valves exist for blasting machines. Such a valve arrangement is illustrated in U.S. Pat. No. 4,802,313, to Smith. The Smith ""313 patent discloses an abrasive control valve featuring an air-actuated piston arrangement. A shaft is connected to the piston at one end while its opposite end features a tip. The valve features a housing that is divided into three chambers: an air chamber, a mixing chamber and the chamber that serves as the cylinder for the sliding piston. The air chamber receives pressurized air and the mixing chamber receives abrasive. The air and mixing chambers are in communication and the latter features an outlet through which a resulting pressurized flow of abrasive may exit the valve. The tip of the shaft is sized to engage the outlet so that the valve may be closed by introducing air into the cylinder on one side of the piston and opened by introducing air into the cylinder on the opposite side of the piston.
The cylinder chamber of the housing in the Smith ""313 patent is divided from the air and mixing chambers by a wall with a cylindrical passage through which the shaft passes. The shaft is provided with a circumferential groove within which an O-ring is secured. The O-ring engages the interior wall of the cylindrical passage in a sliding fashion to prevent abrasive from the air and mixing chambers entering the cylinder chamber. A disadvantage of such an arrangement, however, is that the O-ring wears due to its sliding engagement with the cylindrical passage. As a result, the O-ring requires frequent replacement.
A further disadvantage of the Smith ""313 patent is that the walls of the mixing chamber disclosed therein do not taper towards the outlet through which the pressurized flow of abrasive passes. This decreases the flow rate of abrasive particles out of the mixing chamber and also increases the wear on the mixing chamber walls.
U.S. Pat. Nos. 2,658,312 and 3,102,368, both to Smith, illustrate spray guns that use a needle valve arrangement to control to delivery of abrasive to a surface or object. Both patents use an air-actuated piston to open or close the needle valve. Both patents also separate the piston cylinder from the abrasive chamber with a wall having a passage through which a shaft passes. The shaft has a tip that engages the valve outlet. In each patent, the passage contains a packing gland assembly to prevent the escape of abrasive from the abrasive chamber into the cylinder. The shaft slides against the packing glands. As a result, the packing glands also suffer wear and require frequent replacement.
An additional disadvantage of the Smith ""312 and ""368 patents is that abrasive entering the valves disclosed therein impacts their needle valve shafts. This may cause points of increased wear to form on the shafts. Furthermore, the valves of the Smith ""312 and ""368 patents feature abrasive chambers that are only slightly larger than their needle valve shafts. This reduces the dispersal of the abrasive particles in the abrasive chambers so that abrasive flow out of the valves is adversely impacted. The reduced dispersal of the abrasive particles also causes increased wear of the shaft and chamber walls.
Accordingly, it is an object of the present invention to provide a particle control valve that does not pinch the hose supplying particles to a machine.
It is another object of the present invention to provide a particle control valve that is capable of performing a large number of operations without maintenance.
It is another object of the present invention to provide a particle control valve that does not permit the escape of particles into the workplace if failure of the valve occurs.
It is another object of the present invention to provide a particle control valve that may serve as a general replacement for pinch type valves in a variety of machines and applications.
It is still another object of the present invention to provide a particle control valve that optimizes the flow of particles therethrough.
It is still another object of the present invention to provide a particle control valve that undergoes less wear of its interior chamber walls, outlet and needle valve shaft when in operation.
The present invention is directed to a particle control valve for controlling the flow of a pressurized powder or particles, such as abrasive media, to a machine or device, such as a blasting machine. Abrasive powder carried in a stream of compressed air is supplied through an angled passage to a valve body that contains a particle/abrasive chamber. A shaft positioned within the abrasive chamber is moved between open and closed positions by an actuating mechanism such as an air piston and cylinder arrangement. On the end of the shaft is a rubber nose piece which seals against a hardened seat when the shaft is in the closed position. When the shaft is in the open position, the nose piece disengages the seat to permit passage of abrasive out of the valve.
A flexible sealed barrier is situated between the valve body and the housing of the piston and cylinder to prevent abrasive from contaminating the piston and cylinder thus creating a xe2x80x9ccleanxe2x80x9d and xe2x80x9cdirtyxe2x80x9d side of the valve. A clean chamber positioned between the piston and cylinder mechanism and the barrier is pressurized with air at generally the same pressure as the abrasive chamber so that the barrier always has generally equal pressure on either side thus minimizing wear of the barrier.
The junction between the angled passage and the abrasive chamber has a larger cross-sectional area than that of the angled passage. The angled passage has a larger cross-sectional area than the input port through which abrasive is delivered to the valve. The velocity of the abrasive particles thus decreases upon entry into the angled passage, and then again upon entry into the abrasive chamber. This eliminates a potential wear point on the shaft and reduces wear on the passage and abrasive chamber walls. In addition, this causes the particles to disperse around the shaft before passing through the valve exit orifice. The dispersal of abrasive around the shaft eliminates a possible concentration of abrasive on one side of the exit orifice. This enables an optimal flow of abrasive out of the valve. The diameter of the abrasive chamber is significantly larger than that of the shaft which also encourages even dispersal of the abrasive around the shaft.
The following detailed description of embodiments of the invention, taken in conjunction with the appended claims and accompanying drawings, provide a more complete understanding of the nature and scope of the invention.